The effective measurement of energy usage can only be obtained if the measuring instruments are accurately calibrated to a proper standard or within acceptable limits of the standard. Improperly calibrated meters result in inaccurate measurements of actual energy usage and introduce an unknown amount of error into any calculations based upon such measurements. In the context of a residential electric meter, accurate measurement of the customer's energy usage is important so that the customer can be properly charged.
Proper calibration of energy meters is not limited to residential electric meters. It is also extremely important for meters used in various other applications, such as in industrial uses and scientific experimentation to, be accurately calibrated. Due to the vast number of industrial and residential meters currently in use, such as watthour meters. Q-hour meters and varmeters, accurate and expeditious calibration techniques are needed to efficiently calibrate large numbers of meters desired to be calibrated and recalibrated.
Conventional methods of calibrating energy meters require that precision currents and potentials be applied to the meter under test so that accurate readings can be obtained. Once connected to the energy source, the rotation of the meter rotor is then accurately timed for an integral number of revolutions. At a minimum, at least one complete revolution of the rotor in the meter is required in conventional measurement systems and more accurate readings are obtained if several complete revolutions are timed. The time period for the rotor of the meter to complete one or more revolutions is then calculated and compared to a standardized time period for acceptable calibration for the type of meter being tested. The difference between the actual and the standard time period is then calculated so that a corresponding adjustment can be made to the meter under test.
After an initial adjustment, the meter must once again be tested to verify accurate adjustment for proper calibration within acceptable limits. This type of conventional testing often requires many individual test runs and corresponding meter adjustments because the calibrating adjustments of the meters are typically not linear. As a result, conventional calibration of energy meters has been an extremely inefficient and time-consuming process. A significant problem is that energy changes or fluctuations during the test procedure result in inaccurate readings which do not properly reflect the extent to which a meter may be out of calibration.
Another conventional system employed in the prior art for calibration of meters involves the use of a reference device to generate a reference signal having a selected frequency which is upplied to a counter. Integral revolutions of the test meter rotor are then used to gate the counter on and off so that the counter functions to count and store the number of reference signal pulses supplied to the counter during one or more integral revolutions of the test meter rotor. This type of system has the inherent inefficiency of requiring one or more complete revolutions of the test meter rotor before calibration adjustment can even be started. Complete revolutions are again required for additional test runs for further calibration.
In accordance with the present invention, a system and a method for calibrating energy meters are provided which eliminate the inefficiencies of conventional systems. The method and system of the present invention do not require precision currents and potentials in order to calibrate the energy meters. In addition, the necessity of timing the rotation of the rotor is eliminated. Adjustment of the energy meters can be effected based upon non-integral revolutions of the test meter rotor and, in fact, proper calibration adjustment can be made upon only a fractional revolution of the test meter rotor, thereby substantially reducing the time required to calibrate the meter.